Full citations of the references appear after the Examples section.
Through careful inspection, intelligence, undercover operation and surveillance, customs and police officers worldwide manage to interdict tons of illicit drugs per year. However, because they are overwhelmingly outnumbered by their adversary, the quantity of seized drugs represents only a fraction of the total volume of the drugs trafficked. The use of large marine containers is a well known smuggling method for large shipments of drugs. Such containers present an ideal method of smuggling as the examination method is time consuming for Customs personnel and costly to the importing community. For these reasons, the interdiction of drugs through marine containers is a high priority item for Customs officials in the U.S., Canada and Western Europe.
To date, the most reliable method for searching containers involves manual unloading of the cargo (de-stuffing) and careful screening of each item by manual inspection. Because of limited resources, relatively few containers can be examined in this manner. Thus, a detection aid allowing rapid pre-screening of the containers is required to distinguish between innocent and suspicious cargo. The fundamental objective of providing technical support to the law enforcement officer is to improve this situation.
In the past, the only known detection aid used in customs work throughout many countries to search out narcotics was the so-called `drugs` dog. Appropriately trained dogs can be an effective means of rapidly examining large quantities of baggage and freight in spite of several drawbacks. A dog can only work for a certain length of time and its enthusiasm and interest can vary.
Accordingly, there has been interest and steady growth in research and development in the field of instruments for the detection of illicit drugs.
Instrumental methods of detecting concealed drugs may be categorized under two main headings, bulk detection techniques and chemical sensing techniques. In bulk detection techniques, suspect items to be examined are subjected to electromagnetic or ionizing radiation and the presence of drugs is determined by the interaction of the bulk content of the item with the probing field. These include X-ray imaging, gamma backscatterring and thermal neutron activation. For example, X-ray examination of loaded cargo containers is being used. However this technique requires very large and expensive facilities; furthermore, X-ray systems provide little in the way of a specific and distinguishing signal for narcotics.
Chemical sensing techniques are based on the chemical analysis of air or wipe samples obtained from within, from the exterior surface or from the vicinity of a suspect item, to determine trace amounts of drugs and/or drug-related constituents. These constituents may be present in the form of vapours or microscopic particles. All chemistry based drug detectors are composed of two parts: a sampler and an analyzer.
The function of the sampler is to collect the drugs, as vapours or particulates, on a filter which is then brought to the inlet of the analyzer where it is heated and analyzed. The analyzers use principles such as ion mobility spectrometry, gas chromatography and mass spectrometry. The sampling strategy and methodology is fundamentally different for preconcentration of vapours and the collection of solids, either airborne or bound to surfaces. This must be taken into account when collecting samples to determine the presence of smuggled cocaine.
Drug detection methods have been developed which rely on the presence of particulates (5-100 microns) for detection of drugs of interest (U.S. Pat. No. 4,580,440, and/or U.S. application No. 08/352,486 U.S. Pat. No. 5,576,976, both of which are incorporated by reference). This method has been used with some success at airports, penitentiaries, land border crossings for small vehicles, at marine ports for boat searches, and at postal plants. When applied to cargo containers, however, the sampling of particulates has limitations:
Particulates may not be present if the cocaine has been packaged carefully. PA1 For effective sampling, the sampling device must come in direct contact with the cocaine particle; this makes particle sampling very site specific within the cargo container. PA1 Particulates can remain in a container for a long period of time and generate alarms in containers previously used for smuggling but no longer holding the contraband. PA1 Cross contamination between the contents of a container can lead to alarms in the wrong area of the container.
Previous work on the vapour pressure of cocaine base 1! showed that, at room temperature, a saturated headspace of cocaine contains approximately 3 ng of cocaine vapors per litre of air. In cargo shipments, however, it is unlikely that conditions will exist to allow the presence of a saturated vapor pressure of cocaine because the smuggled drug consists mainly of cocaine hydrochloride whose vapor pressure is lower than that of cocaine base. Furthermore, the salt of cocaine is normally enclosed in a wrapping material which would hinder the escape of vapors.
A system for the detection of organic vapors in air that are then adsorbed onto a film of fullerenes on a metallic substrate, and released for their detection is disclosed in U.S. Pat. No. 5,395,589 (Inventor: Nacson S; issued Mar. 7, 1995). In U.S. Pat. No. 5,426,056 (issued Mar. 8, 1995) Nacson also discloses a detector for analyzing ionized organic molecule vapors within a sample. The detection of residues from samples by gas chromatography is disclosed in U.S. Pat. No. 5,142,144 (inventor Remo J L, and Turner R.; issued Aug. 25, 1992).
The collection of vapors of nitrogen-containing compounds involving a plurality of open-ended small diameter tubes coated with silicone to trap these vapors and release the vapor upon heating for subsequent detection by gas chromatography is taught in U.S. Pat. No. 5,092,156 (inventor Miskolczy G; issued Mar. 3, 1992).
Although illicit cocaine samples have been shown to emit other vapors such as acetone (a product associated with the manufacture of cocaine), methyl benzoate, benzoic acid (both are decomposition products of cocaine, see (9)) and lidocaine (a cutting agent), such vapors may also be emitted by other licit products, and if the screening processes were based on the detection of these vapors, this might result in high false alarm rates (U.S. Pat. No. 4,580,440).
Ideally, the detection of cocaine would be verified by detecting another compound that is associated with cocaine, but one that is not typically found in association with other chemicals. Furthermore, the associated compound would have a similar or greater volatility (vapor pressure) to cocaine. The ideal cocaine-related compound would also dissipate readily from within a container so that the co-detection of cocaine along with this related compound would ensure the occurrence of cocaine within the container.
The inventors have discovered that many cocaine seized samples not only emit relatively small amounts of cocaine vapors but, more importantly, emit vapors of ecgonidine methyl ester (EDME), a well known structurally related degradation product of cocaine comprised of a bicyclic skeleton. Although EDME has been observed previously in GC-MS analyses of solutions of seized cocaine samples 5,6!, it has never been reported in the vapor phase. We have observed that the vapor pressure of EDME is larger than that of cocaine by 5 orders of magnitude (23000 ppb vs 0.25 ppb) at room temperature. Therefore, the high vapor pressure of EDME makes it a likely candidate for detection by trapping vapors from a cargo container. Due to the increased vapor pressure of EDME, this chemical disappears more rapidly than the vapors associated with cocaine from within a container. Therefore, the detection of both cocaine and EDME vapors provide a reliable indicator, by reducing the number of false positives, of the presence of cocaine within the sampled container.